As is well known, particularly in the field of design, computerized modelling, and publishing, the problem of obtaining a program for controlling machine-tools often arises, for example, in the manufacture of a die by working with a numerical control profile-copying machine directly on a model of the article to be produced. If the model is a physical reproduction of the article, the program should be generated by means of digital encoding of the model itself. In that case, the fundamental requirement is to achieve rapid and reliable digital encoding. A typical application for program processing is that of producing the two halves (male and female) of a die directly from a single digital encoding of the model.
Depending on the technical specifications, one of three methods has typically been used: the profile-copying method; the data collection and storage method; and the method involving digital encoding with a measuring device. However, all these methods present various problems which limit the advantages of their utilization, including those discussed below.
The profile-copying method has the advantage of not requiring dedicated digital encoding equipment. This is because a probe is utilized on the manufacturing equipment, scans the surface of the model, and provides direct control of the profile-copying machine. However, this method has the disadvantages of producing only one die for each scan of the model, of having the speed of the profile-copying machine limited by the relatively slow scanning speed of the probe, and of having the precision of scanning reduced by vibrations associated with the manufacturing process. The profile-copying method is also unable to compensate for the shape and the errors of the probe, since the fabrication process proceeds simultaneously with the data collection phase.
As a result, it is necessary to change the probe and repeat the model scanning procedure for each phase of the fabrication process.
The data collection and storage method also uses a profile-copying machine as its basic equipment, but the process is divided into two parts: digital encoding and fabrication. A device control unit actually controls the first process, digital encoding of the model, using a profile-copying machine and its probe at the highest speed allowed by the probe itself, and the results are stored on a data storage disk. The same unit subsequently controls the machine during the milling phase at the maximum speed allowed by the machine tool, utilizing the data stored previously. In this instance, the scanning phase represents 20-30% of the total time for the process, and the data collected from the model may be used for several fabrication sequences. However, the use of the profile-copying machine for scanning the model, thereby diverting it from the fabrication process, is not efficient or cost-effective.
The method involving digital encoding with a measuring device uses a dedicated machine to digitally encode the model and to generate the program for controlling further profile-copying. The scanning data is processed by a computer which optimizes the cutting path and derives the programs for roughing out, preliminary finishing, and finishing from the same set of scanning data. The same measuring device can then be used to control the dimensions of the final product. With this method, maximum utilization of machine tools is achieved, since they can function continuously at maximum capacity. One of the principal limitations of this method is the low speed of digital encoding, owing to the need to capture all the details required for precise control of the profiling machine during the finishing phase, and owing to the need to rotate the probe. Also, the cost of the system is high, owing to the dimensions of the machine and of the probe configuration; and the precision is low, owing to the impossibility of adjusting for the dimensions of the probe in space. The process is also relatively incomplete, permitting processing only of the data received from the physical model. However, this last limitation is shared by all the other methods described above.
It is an object of the present invention to obviate the above-indicated shortcomings in known systems for modelling physical articles. These shortcomings are primarily limitations in effectiveness due to the slowness of the digital encoding process, insufficient processing capacity for the data collected, and the inability to interface on-line with projection (e.g. through extrapolation) and manufacturing systems supported by a (CAD/CAM) computer for the definition of parts of the die which are not present in the physical model.
In accordance with the present invention, an interactive system for modelling physical articles includes a measuring device, and processing means. At least initial identification data for the article are provided via the measuring device to the processing means, and the processing means produces automatic signals to control the measuring device in acquiring additional data regarding the model. The processing means utilizes the data to generate a model representing the article shape and dimensions in the form of signals usable for program controlled apparatus, such as machine-tools.
In accordance with the method of the invention, the surface of the article to be modelled is divided into one or more areas called "patches", for example, by the operator specifying a set of control coordinates roughly defining the boundary of each patch. The machine is then operated to control the probe so as to acquire measurements at additional points necessary to define the boundaries with a specified degree of accuracy, and the boundaries are modelled with a set of contour-defining equations which minimize the deviation from the measured points. Thereafter, the surface of each patch on the article is measured at selected points, the results are compared to the values derived from the modelling equations at the same points, and the equations are modified to minimize deviations of the model from measured points. This process of measuring, comparing measured points with the model, and refining the model continues, until a model with a desired degree of accuracy is derived by successive approximation.